The long-term objective of this project address the surprising fact that human influenza is rarely, if ever, associated with etiologically proved neurological complications. In this respect, influenza seems to differ from human illnesses caused by viruses representing virtually every other taxonomic family. Actually, a case can be made for the idea that influenza viruses, which are genetically more variable than most others, have in the past, and may again, appear in the form of strains with uniquely high intrinsic virulence. It seems possible that such stains (cf. the 1918-19 strain) may cause violent, systemic illnesses with involvement of the central nervous system (CNS), as avian strains do in birds and, recently, in mammals (seals). Moreover, the almost 10-fold increased incidence of Guillain-Barre Syndrome associated with "swine flu" immunization has led to the suggestion that the inactivated A/NJ/76 strain (HswN1) and even its split products may be unusual in the ability to induce immunologically mediated neuropathology. The model systems are mice of different ages and mouse embryo brain (MEB) cell cultures at various levels of differentiation: specialized cells such as neurons, astrocytes, oligodendrocytes (ODC), cerebral endothelial cells, and fibroblasts respond with varying expression of specific viral gene products, specifically M1 and NS1 proteins, to "non-neurovirulent" strains A/PR/8/34 (PR8) or A/WS/33 (Ws), in contrast to the neurovirulent derivative WSN. The specific aims are to (1) analyze mechanisms of M1 and NS1 (but not M2 and NS2) restriction in PR8-infected astrocyte-enriched MEB cultures in terms of transcriptional (specifically >spliced/unspliced mRNAs) or translational (e.g. >protein kinase) control; (2) assess the significance and duration of NP persistence in PR8-infected astrocytes and ability of NP(+) cells to divide; (3) look for trans-synaptic transfer of viral genomes and proteins; (4) test for evidence of changes in myelin components and, in vivo, demyelination; (5) specifically, test for presentation of viral neuraminidase on axonal or ODC membranes resulting in desialylation and los of myelin-assoc.glycoprotein; (6) continue detailed study of viral replication in brain endothelial cells, including possible changes in MHC Ag presentation in vitro and in vivo; (7) similarly, examine differentiated CNS or PNS cells for presentation of new MHC Ag's in response to virus, viral components, or virus-induced interferon(s), as a measure of directly or indirectly virus- mediated activation of H/I T cells and autoimmune phenomena; (8) challenge mice that have survived CNS infection after intranasal inoculation as sucklings, by i.v. or i.p. inoculation, at various times, of the same or different strains or subtypes and monitor for neuropathology.